In recent years, there has been a steady increase in the number of airplanes in service at any one time. With this rise in the number of aircraft, there has been an increased interest in minimizing the separation distance between airplanes without compromising safety. Additionally, there is a trend towards autonomous or free-flight planning wherein the pilot, while en route, will be permitted to change the aircraft's flight plan. In order to accomplish these and other objectives, it is desirable for air traffic controllers and pilots to know, as precisely as possible, the location of all airplanes relative to one another.
Typically, several sensor systems including radar systems, beacon systems, etc., are employed for surveillance and tracking, along with current position reports from pilots, estimations based on flight plans and vehicle speed, etc. These methods are imprecise and limited in that they individually report different approximate positions for the same object such as an airborne aircraft, and a margin of error must be applied to each reported location. These differences in the reported locations and errors arise because of the performance and operational characteristics of the sensors, and the prevailing environmental conditions. For example, the reliability of information from a radar system, no matter how sophisticated, might vary greatly with atmospheric conditions, most likely being more precise under clear and calm conditions than under stormy conditions (rain, snow, hail, etc.). The margin of error, when applied to each quantitative and qualitative observation, results in the tracking system applying a larger than desirable separation zone around the best estimated aircraft location. This separation zone, or uncertainty zone, is typically increased during foul weather in order to compensate for the performance characteristics of the sensors and the less than optimal reliability and accuracy of the data.
Such existing methods and systems for locating an object are generally directed towards guiding an aircraft onto the runway when landing. Other systems, such as the Traffic Alert and Collision Avoidance System (TCAS) issue alerts and evasive commands only after the safety zone has been breached. The TCAS relies on data transmitted by a transponder located on an aircraft. Since all aircraft are not mandated to have a transponder, the system can not be relied upon for maintaining minimum and safe separation zones. Other current methods collect data from several sources, and then report the location information either by applying a weighted average to the data, or relaying the data from a single sensor, or transmitting all information as separate attributes (e.g., speed, direction, altitude, etc.).
Therefore, there exists a need for a method and apparatus to collect all available quantitative and qualitative data from the numerous sources and aggregate these with prior knowledge of their performance characteristics to more accurately locate and track an object such as an airborne aircraft.